At least 18 people have been killed in an apparent suicide bombing at a Muslim shrine in Pakistan, rescuers say.
The condition of many of the injured is serious
Hundreds of Shias had gathered at the Bari Imam shrine on the outskirts of the capital, Islamabad, to celebrate the end of a religious festival.
More than 50 people were hurt in the blast. Correspondents said the scene was one of utter carnage, with bodies and body parts strewn around the area.
Pakistan has a history of conflict between Sunni and Shia extremists.
Information Minister Sheikh Rashid Ahmed said it was too early to say who was to blame for the attack. No group has said it carried it out.
Ambulance crews have been ferrying survivors to hospital following Friday's blast, which occurred at about 1120 (0620 GMT).
They said they had recovered nearly 20 bodies but survivors said the figure was much higher.
Many of the injured are said to be in a serious condition.
The shrine is near Pakistan's main government buildings and Islamabad's diplomatic quarter, where many countries have their embassies.
Police swiftly cordoned off the blast site.
March 2005: 43 Shias killed in a bomb blast in Fatehpur, Baluchistan
Oct 2004: Car bomb in Multan kills 40 Sunnis
Oct 2004: 30 killed in a suicide attack on a Sialkot Shia mosque
May 2004: 20 killed in bombing of Shia mosque in Karachi
May 2004: 15 die in Karachi Shia mosque attack
"Our initial information suggests it was a suicide attack," said Islamabad police chief Talat Mehmood Tariq.
Survivors said the bomber, who joined a congregation of about 1,000 people attending a sermon, triggered explosive devices strapped to his waist.
"We were listening to a sermon when there was a huge blast," one survivor, Munazar Abbasi, is quoted as saying by Reuters.
"Everything went blank and I couldn't hear anything."
Many of those who survived were shocked and angry, some calling the attack an act of terrorism by members of the Sunni majority.
Amongst the crowds gathered, many men pounded their chests in grief as blood-stained bodies covered with religious banners were taken away.
President Pervez Musharraf expressed shock and grief at the loss of life, the official APP news agency reported.
The BBC's Zaffar Abbas at the scene in Islamabad says it is the first time the Bari Imam shrine has been targeted.
PAKISTAN'S SECTARIAN DIVIDE
Shias revere Ali, son-in-law of the Prophet Mohammed
Pakistan is 20% Shia, 70% Sunni
Violence between Sunni and Shia factions began in early 1980s
More than 150 people have died in the past year alone
About 4,000 people have been killed in total
Most violence takes place in Sindh, Balochistan and Punjab
Our correspondent says the Bara Imam shrine honoured a popular Sufi saint and was visited by many Sunnis as well as minority Shias.
He says it was seen as a symbol of harmony between the two communities.
The shrine was the scene of violence in February of this year, when its custodian Raja Akram and his bodyguard were killed in an ambush which police described as family rivalry.
One of the attackers was also killed when Raja Akram's bodyguard returned fire, police said.
Pakistan has a long history of sectarian violence between Sunnis and Shias.
More than 40 people were killed and many injured in a bomb blast at a Muslim shrine in the south of the country in March.
About 4,000 people have been killed over the past several years.